1. Field of the Invention
This invention relates to determining, from a telephone central office, whether or not a telephone is in used by a subscriber.
2. Description of the Prior Art
A frequent telephone problem is where a first subscriber reports repeated busy signals when trying to reach a second subscriber. Assuming the first subscriber has dialed correctly, busy signals may be produced by a leakage path between the second subscriber's telephone line conductors or by the second subscriber's telephone being in a receiver-off-hook-and-in-use condition or in a receiver-off-hook-and-not-in-use condition.
Heretofore, it has been a common practice to identify the cause of the problem by an operator or craftsperson gaining access to the line in question and listening. When any one of a number of signals is heard, an in-use condition exists. Such signals include TOUCH-TONE.RTM.or rotary dialing signals (indicating that the second subscriber is signaling), a busy signal (indicating that the second subscriber has dialed and is receiving a busy signal), ringing signals (indicating that the second subscriber has dialed and that a called party's phone is ringing) and, of course, speech signals.
On the other hand, when a dial tone is heard, it is known that a receiver is off-hook and not in use (i.e., dialing not attempted). Furthermore, a holding trunk tone indicates either a line short or a receiver off-hook and no-dialing-attempted condition. Still further, a dead or quiet line indicates a low impedance short across the line conductors while a noise "signal" indicates a higher impedance leakage path across the line conductors.
The above-described testing procedure requires what is considered to be an unreasonable length of time for testing, possible ambiguity with respect to the results produced and, furthermore, possible interference with a customer's conversation. In an effort to circumvent these undersirable characteristics, consideration has been given to automating the entire test procedure.